This invention relates to a manifold and in particular to a four-valve manifold.
Valve manifolds of the type described herein are, for example, used in fluid process instruments such as flow meters when it is a requirement that fluid be introduced into the instrument simultaneously through two lines. In general, three and five valve manifolds are used for such purpose. Examples of such valves are found in U.S. Pat. Nos. 4,092,865 issued to R. V. Strybel on Jun. 6, 1978; 4,109,536 issued to R. V. Strybel on Aug. 29, 1978 and 4,319,492 issued to J. E. Hewson et al on Mar. 16, 1982.
Currently available three and five valve manifolds possess certain disadvantages. The three valve manifold usually includes two line block valves and an equalizer valve. In order to vent or evacuate process fluid from the manifold it is necessary to remove the main input line from the manifold, i.e. to crack open the coupling used to connect the main input line to the manifold. Such a method of venting can expose the user to potentially dangerous fluids. Moreover, the equalization valve of the three valve manifold cannot readily be checked for leakage from the high to the low pressure side thereof. When using the manifold with a flow meter, leakages of this type may result in the inaccurate flow measurement of the process medium at the recording instrument. Another disadvantage of venting the manifold in the above described manner is that if the equalizing valve should remain closed an unbalancing effect of the fluid will be applied to the recording instrument, which may result in damage to the latter.
The five valve manifold was introduced in an attempt to overcome the problems encountered with the three valve manifold. By increasing the number of valves from three to five there is a substantial increase in manufacturing costs. The introduction of two equalizer valves and one vent valve in the five valve manifold solved the problem of leaks between the high and low pressure side of the manifold, but a problem may still exist when the manifold is vented, i.e. process fluid is evacuated. As with the three valve manifold, the equalizer valve must be in the open position during evacuation of the process pressure, otherwise there may be extensive damage to the recording instrument. Moreover, in order to evacuate a five valve manifold both of the equalizing valves must be open. If the operator fails to open both valves, i.e. opens only one valve, unbalanced pressure will be applied to the recording instrument with possible damage to the instrument.
The object of the present invention is to overcome the above mentioned disadvantages by providing a simple four valve manifold, which possesses the advantages of the five valve manifold, at a lower cost.